Method of Processing and Treatment of Alunite Ores

ABSTRACT

The alunite ore processing method consists of crushing, grinding and flotation of raw alunite ore. The enriched alunite ore is roasted at 520 to 620° C., the roasting time is 1 to 3 hours. The roasted alunite is leached with 5 to 20% sodium carbonate solution, which is in 100 to 110% of the stoichiometric amount required to bond the SO 3  aluminum sulfate in the alunite with leaching conditions of 70-100° C. for 0.5-2.0 hours. The obtained slurry contains all of the potassium sulfate from the alunite and all of the sodium sulfate obtained from sodium carbonate. In the insoluble residue remains all aluminium oxide and residual rock. The sulfate solution is separated from the insoluble residue and is converted with potassium chloride to potassium sulphate (fertilizer) and kitchen salt. The insoluble residue is treated by the Bayer method without the use of an autoclave and results in aluminium oxide (alumina) and quartz sand.

TECHNICAL FIELD

This invention relates to/concerns technology of alunite ore processingresulting in the production of γ-Al₂O₃ with the production of fertilizerpotassium sulfate, kitchen salt, metallurgical aluminum oxide and quartzsand.

BACKGROUND ART

Alunite is a raw material for the aluminum and chemical industries.Industrial alunite ore deposits are common in the USA, China,Azerbaijan, Iran, Mexico, Kazakhstan, Ukraine, Russia and othercountries. The presented invention concerns the processing of aluniteore with the production of fertilizer potassium sulphate, kitchen salt,metallurgical alumina and quartz sand.

An alkaline reduction method for processing alunite ore [1] is known.This method was used in the Ganja Aluminum Combine (GGC). Due tosignificant technological drawbacks (such as low alumina yield of lessthan 70 pollution of the environment by dust and gas, a need for rareand expensive raw materials, large quantities of solid waste from 5 tonsper 1 ton of alumina and an undesirable by-product sulfuric acid) GGCceased its operations in 1992 and to this date does not operate.

A method for processing of alunite ore was developed for the productionof potassium fertilizers (SOP), sulfuric acid, alumina and quartz sandin Utah (USA) [2]. In this method, the alunite ore is roasted at 600° C.or lower with the release of SO₂, which leads to the production ofsulfuric acid, and the roasted alunite is extracted with hot water toproduce K₂SO₄ (SOP). A reducing agent (excess oil or elemental sulfurvapors) should be introduced during roasting in order to acquire entireSO₂ aluminium sulphate. The combustion temperature of 600° C. allows topreserve γ-Al₂O₃ in an active form. However, leaching (in hot water at80 to 99° C.) of the alunite T≤600° C. results in the loss of SOPs dueto the formation of water-insoluble basic salts. The yield of SOP in thesolution does not exceed 65 to 70%. Roasting of the alunite at 800 to900° C. improves SOP yield to almost 100%, while γ-Al₂O₃ is convertedinto an insoluble form of α-Al₂O₃. There is no floatation method thatcan divide α-Al₂O₃ and quartz the insoluble residue in order to obtainmetallurgical alumina.

The drawbacks were eliminated by the potash-alkaline method(Liner-Taghiyev) [3, 4, 5, 7], where the alunite roasted at thetemperature of T≤550° C. was leached with potassium carbonate solutionaccording to the reaction:

K₂SO₄.Al₂(SO₄)₃.2Al₂O₃ +nn+3K₂CO₃=4K₂SO₄+3Al₂O₃ +nn+3CO₂(nn−waste rock).

Up to 4 times more SOP and alumina (γ-Al₂O₃) is transferred into thesolution, the metallurgical-Al₂O₃ remains in the insoluble residue. TheSOP is obtained from the solution and the insoluble residue is processedby the Bayer method by means of leaching with the recycled solution ofaluminate at T=80-90° C. to obtain metallurgical alumina and quartzsand. The disadvantage of this method is the use of a rare and expensive(including USA) potassium carbonate.

The foregoing drawbacks are addressed by the invention below.

The state of the art is further described in the following literature:

-   1. G. V. Labutin Recovery method for the processing of alunite.    Autor. Svid. USSR No. 9911 a No. 108947 from year 1948.-   2. Internet. Potash Ridge Corp. Technical report. Dated 24 Apr. 2017    Project No. 17M16.-   3. A. I. Liner, V. I. Zakharova, Yu. A. Layner, El Taghiyev, Z.    Pevzner Autor. Svid. SSSR No. 460709 d. 21 Oct. 1974.-   4. E. I. Tagijev, patent of the Republic of Azerbaijan I 2001 0142    dated 2 Oct. 2001.-   5. E. I. Tagijev, patent of the Republic of Azerbaijan I 2003 0210    dated 30 Oct. 2003.-   6. E. I. Tagijev, I. S. Babayev, S. B. Rajabli, A. T. Khudiev, T. B.    Aliyev Autofi. Svid. SSSR 5 No. 872456 dated 15 Jun. 1981.-   7. E. I. Tagijev, Technology Of Complex Waste-fee Processing Of    Alunite Ores. Baku, Elm, 2006, 504 pages (research monograph in    Russian).

SUMMARY OF THE INVENTION

The processing of the alunite ore (alunite) consists first of the knownsteps: crushing, grinding and flotation of alunite ore. Flotation of thealunite ore proceeds with a flotoreagent and is proposed in the methodaccording to the state of the art, point 2. The enriched alunite orecontaining 25-95% preferably 60% of mineral alunite is further roastedat a temperature of 520 to 620° C., the roasting time is 1 to 3 hours.The roasted alunite, in accordance with the present invention, isfurther leached with 5 to 20% sodium carbonate solution, which is addedin an amount of 100 to 110% of the stoichiometric amount required tobond the SO₃ aluminium sulphate in the alunite, that is Na₂CO₃ is addedin an excess of 0 to 10% over the calculated stoichiometric coefficientsof the reaction equation 1, at 70-100° C. for 0.5 to 2.0 hours. Theobtained slurry solution contains all potassium sulphate from aluniteand sodium sulphate obtained from sodium carbonate. In the insolubleresidue remains all of aluminium oxide from alunite and waste rock,where the waste rock is silica-SiO₂ and clay (aluminum) aluminosilicate.The sulfate solution is further separated by either filtration orprecipitation from an insoluble residue and is converted with potassiumchloride to potassium sulphate (fertilizer) and kitchen salt. Theinsoluble residue is processed by the Bayer method without autoclavingand at a temperature of less than 100° C. to form aluminium oxide(alumina) and quartz sand.

In order to overcome the disadvantages of the prior art, it is proposedto replace the solution of potassium carbonate with a solution ofcalcined soda (1) and then to convert right after the first leaching theobtained sodium sulphate by the conversion method with KCl to potassiumsulphate (fertilizer) and sodium chloride NaCl (2), which is thebasic/fundamental inventive idea of this invention.

K₂SO₄.Al₂(SO₄)₃.2Al₂O₃ +nn+3Na₂CO₃=K₂SO₄+3Na₂SO₄+3Al₂O₃+nn+3CO₂  Reaction (1):

K₂SO₄+3Na₂SO₄+6KCl=4K₂SO₄+6NaCl,  Reaction (2):

3Al₂O₃+nn is the insoluble residue, which is processed by the Bayermethod without autoclaving to form aluminium oxide (alumina) and quartzsand. Alunite is roasted at 520 to 620° C., the time of roasting is 1 to3 hours.

The roasted alunite is leached with 5 to 20% sodium carbonate solutionin an amount of 100 to 110% of the stoichiometric amount required tobond the SO₃ aluminium sulphate in the alunite, that is Na₂CO₃ is addedin an excess of 0 to 10% over the calculated stoichiometric coefficientsof the reaction equation at 70 to 100° C. for 0.5 to 2.0 hours.

The products of this process are: K₂SO₄— fertilizer, NaCl—kitchen salt,Al₂O₃— metallurgical, SiO₂— quartz sand and coagulant for waterpurification [6].

Note: The United States is the second largest producer of sodiumcarbonate in the world, and Canada is the world's largest producer ofpotassium chloride (KCl).

EXAMPLES OF EMBODIMENTS OF THE INVENTION Example 1

We take an alunite ore with an alunite content of 60% by weight, withthe following composition, % by weight:

K₂O Al₂O₃ SO₃ H₂O nn Σ 6.82 22.17 23.18 7.82 40 99.9

100 g of alunite (alumina) is crushed. Alunite (alunite ore) is furthergrinded, after the flotation enrichment it is roasted in an oven atT=550° C. for 1 hour and then leached in the solution of Na₂CO₃.

A sodium salt solution is prepared: 22.2 g of Na₂CO₃ is dissolved in 350ml of water, the amount of soda is 105% wt. from stoichiometric. Theleaching time is 1.5 hours at T_(leach) 90° C.

Into solution are transferred: K₂O—99% by weight; Na₂CO₃-100% by weight;Al₂O₃— 0.5% wt.; SO3—9 8% wt. or K₂O=6.8 g, Na₂O=13 g, SO₃=2.3 g,Al₂O₃=0.1 g.

In the insoluble residue remains 62.2 g. CO₂ gas is formed.

The suspension is filtered and washed.

The filtrate with the washing water is evaporated.

We obtain a mixture of sulphates K, Na, where the sulphate K is 12.5 g,Na sulphate—29.8 g, the total of 42.3 g of the mixture. This is amixture of sulphates obtained from the evaporated mixture of thefiltrate and washed water.

It is required 23.7 g of KCl to produce 29.8 g of Na₂SO₄. This isreaction number 2: K₂SO₄+3Na₂SO₄+6KCl=4K₂SO₄+6NaCl, with K₂SO₄ alreadypresent in the alunite in the amount of 12.5 g.

The result is 36.6 g of K₂SO₄ plus 12.5 g of K₂SO₄ from alunite. Totalof 49 g of K₂SO₄ and NaCl of 16.8 g.

Example 2

The method of treating the alunite ore consists of the following steps:

-   -   1. The alunite ore from the mine is crushed resulting in        particles of 10 to 20 mm in size.    -   2. Followed by wet milling with a resulting particle size of the        resulting powder under 0.074 micron (passed through a 200 mesh).    -   3. Enrichment of the ground alunite ore by means of flotation.        The resulting weight of the enriched ore containing 60% of        alunite is 5.02 t.    -   4. Drying and roasting of the enriched alunite ore from step 3        at 530 to 550° C. for one hour. After drying and roasting, the        weight of alunite ore is 4.63 tons.    -   5. A solution from 1.12 t of Na₂CO₃ (100%) is prepared, the        solution is prepared in a 5% excess over the stoichiometric        balance of equation (1).

K₂SO₄.Al₂(SO4)₃.2Al₂O₃+waste rock+3Na₂CO₃=K₂SO₄+3Na₂SO₄+3Al₂O₃+wasterock+3CO₂,  (1)

where 3Al₂O₃+waste rock is the insoluble residue. The waste rockcontains silica, silica sand (SiO₂) and aluminosilicate (alumosilicate).

-   -   6. The enriched alunite ore, after drying and roasting from step        4, is leached in a solution of Na₂CO₃ prepared according to step        5 for 1.5 hours at 90° C. in the course of the reaction (1).    -   7. The slurry suspension from leaching (step 6) is filtered and        the filter cake is washed. 2.133 t of solution for evaporation        is formed (mother liquors containing Na₂SO₄ and K₂SO₄ and an        insoluble residue).    -   8. The water after the washing of the cake can be used to        prepare the solution of Na₂CO₃. The mother liquors from step 7        are evaporated/concentrated and converted according to the        reaction (2) to K₂SO₄ fertilizer (2.47 t) and kitchen salt NaCl        (0.845 t).

K₂SO₄+3Na₂SO₄+6KCl=4K₂SO₄+6NaCl  (2)

1.19 t of KCl is used for the conversion.

-   -   9. The insoluble residue from step 5 (3Al₂O₃+waste rock) is        processed by the Bayer method according to the reaction (3)        without using an autoclave at a temperature below 100° C. 0.05 t        of NaOH and the working solution are introduced into the        reaction.

Al₂O₃+2NaOH=2NaAlO₂+H₂O.  (3)

Aluminium oxide (alumina) is formed and remains unchanged “waste rock”,i.e. silica sand (SiO₂) and aluminosilicate.

-   -   10. The products from step 9 are hydroseparated into the sand        fraction and the clay fraction (aluminosilicate and alumina).    -   11. The clay fraction from step 10 is precipitated and the        filter cake is rinsed, with the formation of sludge in the        sediment and the supernatant.    -   12. The sand fraction is washed and filtered to form the silica        sand (2.0 t) and the filtrate.    -   13. The filtrate after filtration of the sand from step 12 and        the supernatant after precipitation of the clay fraction from        step 11 are combined. Thusly formed solution undergoes        desilication to form a white sludge and aluminate solution        (supernatant).    -   14. A reaction of the white sludge with H₂SO₄ (0.05 t) gives the        coagulant from the white sludge (0.33 t).    -   15. The solution of aluminates resulting from the desilication        from step 13 is further decomposed to form Al(OH)₃ and the        mother liquor. The mother liquor may be further evaporated to        form a working solution which may enter step 9 (re-concentration        and recycling of water).

16. One ton of γ-Al₂O₃ is formed by calcination of Al(OH)₃.

BRIEF DESCRIPTION OF DRAWINGS

Diagram in FIG. 1 shows the method for processing and treating ofalunite ores.

ADVANTAGES OF THE INVENTION OVER THE PRIOR ART

-   -   Production of metallurgical aluminium oxide (alumina, Al₂O₃)        reaches 90    -   The amount of SOP produced is increased 4 times, with a yield of        90%.    -   Procedures that pollute the environment with dust and gas (SO₂)        are eliminated.    -   There is no need to use precious and expensive raw materials.    -   This method is in fact free of solid waste.    -   In addition to the efficient production of metallurgical        aluminite and SOP, this method allows to simultaneously produce        other products: kitchen salt, quartz sand and coagulant for        cleaning potable and industrial water.

INDUSTRIAL APPLICABILITY

According to the present invention, the method for the treatment ofalunite is used to treat alunite ores with the production of Al₂O₃, aswell as potassium sulphate, quartz sand, utility and potable waterpurification coagulant and kitchen salt as a by-product.

1. Process for the treatment of alunite ores comprises the followingsteps: crushing of alunite ore, grinding the alunite ore, enrichment ofthe alunite ore by flotation to the content of at least 50% of aluniteby weight, roasting at 520 to 620° C. for 1 to 3 hours, preparation of asodium carbonate solution, which is later used in a leaching processcharacterized in that the sodium carbonate solution comprises 5 to 20%sodium carbonate solution and is added to the alunite ore in a quantityof 100 to 110% of the stoichiometric amount required to bond the SO₃ tothe aluminum sulphate in the alunite ore, thereby forming a sodiumsulphite solution, separation of the sodium sulphate solution from aninsoluble residue, conversion of the sodium sulphate with KCl topotassium sulphate and sodium chloride to form a suspension, filtrationand washing of the suspension to form a filtrate and washing water,evaporation of the filtrate and of the washing water, and treating theinsoluble residue by the Bayer method without the use of an autoclave toform a product comprising aluminium oxide (alumina) and quartz sand. 2.The process of the treatment of alunite ores according to claim 1,characterized in that the solution of Na₂CO₃ is prepared in a 5% excessover the stoichiometric balance of the following equation:Al₂(SO₄)₃.2Al₂O₃+waste rock+3Na₂CO₃=K₂SO₄+3Na₂SO₄+3Al₂O₃+wasterock+3CO₂, where 3Al₂O₃+waste rock is the insoluble residue andcomprises one or more of silica, silica sand (SiO₂) and aluminosilicate.3. The process of the treatment of alunite ores according to claim 1,characterized in that the leaching is carried out at a temperature of 70to 100° C. tor 0.5 to 2.0 hours during the course of a reactioncharacterized by the equation according to claim
 2. 4. The process ofthe treatment of alunite ores according to claim 3, characterized inthat the Bayer method without the use of an autoclave takes place withNaOH at a temperature below 100° C.
 5. The process of the treatment ofalunite ores according to claim 4, characterized in that the productfrom the Bayer method is processed by hydroseparation to produce a sandfraction comprising aluminosilicate and a clay fraction comprisingγ-Al₂O₃.
 6. The process of the treatment of alunite ores according toclaim 5, characterized in that the clay fraction is precipitated to forma cake, which is washed, thereby forming a sludge in a resultingsediment and a resulting supernatant.
 7. The process of the treatment ofalunite ores according to claim 6, characterized in that the sandfraction formed by the hydroseparation is washed and filtered to producesilica sand and a filtrate.
 8. The process of the treatment of aluniteores according to claim 7, characterized in that the filtrate after thefiltration of the sand fraction and the supernatant after theprecipitation of the clay fraction are combined and to form a solution,which undergoes desilication to form a white sludge and an aluminatesolution.
 9. The process of the treatment of alunite ores according toclaim 8, characterized in that a reaction of the white sludge withsulfuric acid results in the formation of a coagulant.
 10. The processof the treatment of alunite ores according to claim 8, characterized indial the supernatant formed from desilication is decomposed to formAl(OH)₃ and a mother liquor, which is further evaporated to form aworking solution which is used as a starting reagent in a second Bayermethod reaction (re-concentration and recycling of water).
 11. Theprocess of the treatment of alunite ores according to claim 10,characterized in that metallurgical γ-Al₂O₃ is formed by the calcinationof Al(OH)₃.
 12. The use of sodium carbonate Na₂CO₃ in the leachingprocess according to claim 1 for the treatment of alunite ores and theproduction of one or more of aluminium oxide potassium sulphate, quartzsand, coagulant for the purification of utility and potable water andkitchen salt.